An application device of this kind is used, for example, for continuously applying seam paste to one of side edge portions of wrapping paper when the wrapping paper travels through a rod-forming section of a cigarette manufacturing machine, the side edge portions forming a lap region of the wrapping paper. The wrapping paper as an object herein receives a shredded tobacco layer on an upper surface thereof and travels through the rod-forming section together with a garniture tape. Thereafter, the seam paste as fluid is applied to the wrapping paper as mentioned above, and then the wrapping paper is bent into a cylindrical form to wrap the shred tobacco layer. Thus, the side edge portions of the wrapping paper forming the lap region are adhered to each other, thereby continuously forming a tobacco rod for cigarette rods.
Methods for applying the seam paste to the wrapping paper in the cigarette manufacturing machine include, for example, a method in which the outer circumferential surface of a rotating disc (paste wheel) is brought into contact with the side edge portion of the wrapping paper to transfer the seam paste onto the wrapping paper through the outer circumferential surface of the rotating disc and a method in which the tip end of a nozzle is brought into contact with the side edge portion of the wrapping paper, and the seam paste is discharged from the tip end of the nozzle and applied to the wrapping paper.
In recent years, with the speedup of operation of a cigarette manufacturing machine, the traveling speed of wrapping paper in a tobacco rod-forming process has been increased, and therefore the flow rate of the seam paste to be applied to the wrapping paper has also been increased. In the former method, the flow rate of application of the seam paste is limited by the rotational speed of the disc. Therefore, the latter method using a nozzle is suitable for the cigarette manufacturing machine of high-speed type.
In the case of a conventional application device using the nozzle, the device includes a tank for storing seam paste therein, the seam paste in the tank is supplied to an application nozzle by means of a feeding device such as a gear pump. The feeding device can not only increase the supply rate of the seam paste but also adjust an application amount of the seam paste to a constant value.
Even if the above-mentioned feeding device such as a gear pump allows quantitative supply, however, there occurs minute pulsation in the discharge pressure of the seam paste for a structural factor of the gear pump. Therefore, the supply amount of the seam paste to the application nozzle slightly fluctuates due to the pulsation, resulting in minute fluctuation of the application amount of the seam paste from the application nozzle to the wrapping paper. On the other hand, since the lap region of the wrapping paper is extremely narrow, it is undesirable that the fluctuation, if only minute one, occur in the amount of the seam paste applied to the wrapping paper. This is because if more seam paste than a proper amount is applied, extra seam paste is forced out when the lap region is formed, and on the other hand, if the seam paste is less than the proper amount, there occurs the problem that the side edge portions of the wrapping paper poorly adhere to each other.
Moreover, in the case of the nozzle used in the application device, the flow velocity of seam paste in the nozzle is greatly heightened due to an increase in the flow rate of the seam paste, so that the nozzle receives a quite large fluid friction. For this reason, the fluid friction causes the base material of the nozzle to corrode at the discharge opening of the nozzle, and after the nozzle has been used over a period of long time, the size of the discharge opening is apt to be undesirably enlarged.
Such enlargement of the discharge opening makes the outflow of seam paste unstable, and thus the application amount of the seam paste is caused to change undesirably.
Consequently, one of the issues in the technical field of a fluid application device is to suppress the fluctuation or change of the application amount of fluid in addition to an improvement in application efficiency.